Concern about microbial contamination of surfaces is widespread, especially in the medical and food industries. Conventional antibacterial agents, including solids, liquids, and gaseous disinfectants based on low molecular weight compounds, suffer from residual toxicity that can lead to equally serious medical and environmental problems. Polymeric antimicrobial materials are non-volatile, more chemically stable, and less likely to permeate skin than their low molecular weight counterparts. Incorporation of antibacterial macromolecules into hydrogels or rubbers, however, does not eliminate residual toxicity behavior. Therefore, covalent attachment of compounds with antibacterial functionalities, such as quaternary ammonium and quaternary phosphonium groups, onto inert polymer surfaces is desirable.
The bactericidal activity of low and high molecular weight antimicrobial agents having quaternary ammonium and quaternary phosphonium groups has been demonstrated. (See S. Tan, G. Li, J. Shen, Y. Liu, M. Zong, J. Appl. Polym. Sci., 77, 1869, (2000); E. R. Kenawy, and G. Wnek, Prog. Polym. Sci., submitted 2002; Y. Chen, X, Wang, B. Li, Series of water-insoluble polymeric quaternary phosphonium salt used for bactericides, U.S. Pat. No. 6,261,538 B1, issued Jul. 17, 2001; C. J. Bradaric-Baus, Y. Zhou, Phosphonium salts and methods for their preparation, International Publication Number: WO 2004/094438 A1, E. R. Kenawy, J. Appl. Polym. Sci., 82, 1364, (2001); E. R. Kenawy and F. I. Abdel, A. R, El-Shansboury, and M. H. El-Newehy, J. Controlled Release, 50,145, (1998); W. K. Whitekettle, G. J. Tafel, Control of protozoa and protozoan cysts that harbor legionella, U.S. Pat. No. 6,579,859, issued Jun. 17, 2003; M. A. Marchisio, P. Bianciardi, T. Longo, P. Ferruti, E. Ranucci, and M. G. Neri, A comparison between the hemolytic and antibacterial activities of new quaternary ammonium polymers, J. Biomater. Sci. Polymer Edn, 6, 533-539 (1994).)
Others have studied the antibacterial activity of polymers having quaternary ammonium and quaternary phosphonium groups. In one study, novel quaternary ammonium polymers were prepared by alkylation of tertiary amino precursors. The antibacterial and hemolytic activities of the polymers were compared with the properties of low molecular weight quaternary ammonium salts. Some of the polymers demonstrated antibacterial activity comparable to the low molecular weight quaternary ammonium compounds but exhibited significantly less or virtually absent hemolytic behavior. (See M. A. Marchisio, P. Bianciardi, T. Longo, P. Ferruti, E. Ranucci, and M. G. Neri, A comparison between the hemolytic and antibacterial activities of new quaternary ammonium polymers, J. Biomater. Sci. Polymer Edn, 6, 533-539 (1994).)
In another study, copolymers synthesized from 2-chloroethyl vinyl ether (CEVE) and methyl methacrylate (MMA), 2-hydroxyethyl methacrylate (HEMA), or vinylbenzyl chloride (VBC) were quaternarized using triethylamine, triphenylphosphine or tributylphosphine and the antibacterial activity of the resulting polycationic biocides was evaluated. (See E. R. Kenawy and Y. A. G. Mahmoud, Synthesis and antimicrobial activity of some linear copolymers with quaternary ammonium and phosphonium groups, Macromol. Biosci. 3, 107-16, (2003).) The phosphonium-containing biocides were more effective against bacteria than the ammonium-containing copolymers. In addition, the antibacterial activity was found to increase as the number of phosphonium units in the copolymer increased. The increase in charge density may facilitate the incorporation of the biocide into bacteria cells, leading to potassium ion leakage and, eventually, cell death.
In another study, the copolymer poly(glycidyl methacrylate-co-2-hydroxyethyl methacrylate) was functionalized with chloromethyl groups using chloroacetyl chloride and subsequently converted to a quaternary ammonium or quaternary phosphonium salt. (See E. R. Kenawy, F. I. Abdel-Hay, A B D El-Raheem, R. El-Shanshoury, and M. H. El-Newehy, Biologically active polymers. V. Synthesis and antimicrobial activity of modified poly(glycidyl methacrylate-co-2-hydroxyethyl methacrylate) derivatives with quaternary ammonium and phosphonium salts, J. Polym. Sci, Part A: Polymer Chemistry, 40, 2384-2393, (2002).) The antibacterial activity of the resulting polycations was evaluated against gram-negative bacteria (Escherichia coli, Pseudonomas aeruginosa, Shigella sp., and Salmonella typhae), gram-positive bacteria (Bacillus subtilus and B. cereus) and fungus (Trichophyton rubrum). All of the copolymers exhibited high antibacterial activity but the quaternary phosphonium salt synthesized from tributylphosphine was the most effective against both gram negative and positive bacteria and the fungus T. rubrum. 
Others have used wet-chemistry techniques to functionalize surfaces with quaternary ammonium and quaternary phosphonium containing compounds. In one study, poly(4-vinyl-N-alkylpyridinum bromide) was covalently attached to glass slides and the antibacterial properties evaluated. (See J. C. Tiller, C. J. Liao, K. Lewis, and A. M. Klibanov, Designing surfaces that kill bacteria on contact, PNAS, 98, 5981-5985, (2001).) Amino glass slides were functionalized by either acylation with acryloyl chloride, graft copolymerization with 4-vinylpyridine, and N-hexylation with hexyl bromide, or by the attachment of partially N-hexylated poly(4-vinylpyridine). The modified surfaces killed more than 90% of S. aureus cells deposited onto the surface of the slides and more than 99% of deposited S. epidermidis, P. aeruginosa, and E. coli cells in a dry state. The antibacterial activity of the surface-bound polycations was thought to be due to the disruption of the outer cell membranes of bacteria and/or penetration of the inner cell membranes followed by leakage of cellular contents.
In another study, wet-chemical techniques were used to graft quaternary phosphonium salts onto macromolecular supports. (See A. Popa, C. M. Davidescu, R. Trif, Gh. Ilia, S. Iliescu, and Gh. Dehelean, Study of quaternary ‘onium’ salts grafted on polymers: antibacterial activity of quaternary phosphonium salts grafted on ‘gel-type’ styrene-divinylbenzene copolymers, Reactive and Functional Polymers, 55, 151-158, (2003).) Various alkyl phosphine derivatives were used to quaternize the support copolymer including triethyl, tributyl, tripropyl, triphenyl, methyldiphenyl, dimethylphenyl, ethyldiphenyl, and diethylphenyl phosphine compounds. All of the modified supports exhibited antibacterial activity against S. aureus, E. coli and P. aeruginosa, although the bactericidal efficiencies depended upon the nature of the alkyl groups connected to the phosphonium ions. Surfaces functionalized with the ethylphosphonium compounds showed the strongest antibacterial activity.
Another study demonstrated that polyethylene slides nanocoated with silica and subsequently derivatized with long-chain poly(vinyl-N-hexylpyridinium) become permanently bactericidal. (See J. Lin, J. C. Tiller, S. B. Lee., K. Lewis, A. M. Klibanov, Insights into bactericidal action of surface-attached poly(vinyl-N-hexylpyridinium) chains, Biotechnology Letters, 24, 801-805, (2002).) The modified polyethylene surfaces were able to kill 90-99% of both airborne and waterborne wild-type and antibiotic-resistant strains of the human pathogen Staphylococcus aureus. 
Finally, a recent review of antibacterial and bacterium adsorbing macromolecules emphasized the importance of polymeric biocides for the development of novel surfaces that kill bacteria on contact. (See T. Tashiro, Antibacterial and bacterium adsorbing macromolecules, Macromol. Mater. Eng, 286, 63-87, (2001).) The article describes the immobilization and antibacterial activity of iodine, quaternary ammonium salts, antibiotics, and other antibacterial groups to macromolecular substrates. The synthesis of polycationic polymers with quaternary ammonium salts, biguanide groups, quaternary pyridium salts, sulphonium salts, phosphonium salts, and other antibacterial groups are also discussed. The use of bacterium adsorbing macromolecules based on poly(4-vinylpyridine-co-divinylbenzene), crosslinked poly(3- and 4-chloromethylated styrene-g-amine), and poly(glycidyl methacrylate-g-amine) as well as filters and microporous membranes coated with quaternized poly(4-vinylpyridine-co-styrene) as disinfectants are also evaluated.
Although the prior art describes the use of wet-chemistry techniques to synthesize bactericidal polymers and to immobilize the polymers on the surface of substrates, the use of non-equilibrium, radio frequency (RF) plasmas to functionalize a wide variety of substrates with quaternary ammonium and quaternary phosphonium groups has not yet been accomplished.